1. Field of the Invention
The present invention relates to a surface mounted type chip antenna for improving signal interfix, and a mobile communication apparatus using the antenna.
2. Description of the Related Art
Recently, development trends of mobile communication terminals have been directed toward miniaturization, light-weight, and multi-functionality. In order to satisfy this trend, circuits and parts, which are installed on the mobile communication terminals, have been miniaturized and made multi-functional. Therefore, antennas of the mobile communication terminals have also been miniaturized and made multi-functional.
Generally, antennas which is used in the mobile communication terminals are divided into two types, i.e., a helical antenna and a planar inverted F-type antenna (referred to as a “PIFA”). The helical antenna is an external antenna, which is fixed to the upper surface of the terminal. The helical antenna is mostly used in combination with a monopole antenna. This combined structure of the helical antenna and the monopole antenna has a length of λ/4. Herein, the monopole antenna is an internal antenna, which is stored within the terminal. The monopole antenna is pulled out, thereby being used as the antenna of the terminal in combination with the external helical antenna.
The combined structure of the helical antenna and the monopole has high gain. However, this combined structure of the helical antenna and the monopole antenna has a low SAR characteristic due to the non-directivity. Herein, the SAR(Specific Absorption Rate) characteristic is an index of harmfulness of an electromagnetic wave to the human body. It is difficult to aesthetically and portably design the appearance of the helical antenna. Further, the monopole antenna requires a storage space within the terminal. Therefore, the combined structure of the helical antenna and the monopole antenna limits the miniaturization of the mobile communication product using this structure. In order to solve these problems, a chip antenna having a low profile structure has been introduced.
FIG. 1 is a schematic view illustrating a principle of operation of a conventional chip antenna. The chip antenna of FIG. 1 is referred to as the planar inverted F-type antenna (PIFA). The name of the chip antenna is due to its shape. As shown in FIG. 1, the chip antenna comprises a radiation patch (RE), a short-circuit pin (GT), a coaxial line (CL), and a ground plate (GND). Herein, power is supplied to the radiation patch (RE) through the coaxial line (CL). The radiation patch (RE) is connected to the ground plate (GND) through the short-circuit pin (GT), thereby performing the impedance matching. It is to be noted that the chip antenna is designed so that the length (L) of the radiation patch (RE) and the height (H) of the antenna are determined by the width (Wp) of the short-circuit pin (GT) and the width (W) of the radiation patch (RE).
In this chip antenna, among beams generated by the induced current to the radiation patch (RE), beams directed toward the ground plate are re-induced, thereby reducing the beams directed toward the human body and improving the SAR characteristic. Further, the beams induced toward the radiation patch (RE) are improved. A microstrip antenna in a square shape, in which the radiation patch is reduced to half that of the aforementioned chip antenna, achieves a lower profile structure, thereby being currently spotlighted. Further, in order to satisfy the trend of multi-functionality, the chip antenna has been variously modified, thereby being particularly developed as a dual band chip antenna, which is usable at multiple frequency bands.
FIG. 2a is a perspective view of a conventional dual band chip antenna, and FIG. 2b is a schematic view of a configuration of a mobile communication apparatus using the conventional dual band chip antenna.
With reference to FIG. 2a, the conventional dual band chip antenna 10 comprises a radiation patch 12 formed in a planar square shape, a short-circuit pin 14 for grounding the radiation patch 12, a power-feeding pin 15 for feeding power to the radiation patch 12, and a dielectric block 11 provided with a ground plate 19. In order to achieve dual band function, an U-type slot may be formed on the radiation patch 12. Herein, the radiation patch 12 is substantially divided into two areas by the slot, thereby inducing the current flowing along the slot to have different lengths so as to resonate in two different frequency bands. Therefore, the dual band chip antenna 10 is operated in two different frequency bands, for example, GSM band and DCS band.
However, recently, the usable frequency band has been variously diversified, i.e., CDMA (Code Division Multiple Access) band (approximately 824˜894 MHz), GPS (Global Positioning System) band (approximately 1,570˜1,580 MHz), PCS (Personal Communication System) band (approximately 1,750˜1,870 MHZ or 1,850˜1,990 MHZ), and BT (Blue Tooth) band (approximately 2,400˜2,480 MHz), thereby requiring a multiple band characteristic more than the dual band characteristic. Therefore, the system using the aforementioned slot is limited in designing the antenna with the multiple band characteristic. Further, since the conventional antenna has a low profile so as to be mounted on the mobile communication terminal, the usable frequency band is narrow. Particularly, the height of the antenna is restricted by the limited width of the terminal of the mobile communication apparatus, thereby further increasing the problem of the narrow frequency band.
The dual band chip antenna 10 of FIG. 2a comprises one feeding port formed on the power-feeding pin 15. Therefore, in case that this dual band chip antenna is installed on a mobile communication apparatus, such as a dual band phone, as shown in FIG. 2b, the mobile communication apparatus requires a band splitting unit 21 for splitting the frequency band from the chip antenna 10 into GPS band and CDMA band. For example, the band splitting unit 21 is a diplexer or a switch. Therefore, it is difficult to miniaturize the mobile communication apparatus using the dual band chip antenna.
In order to solve the problem of the narrow frequency bandwidth, a distribution circuit such as a chip-type LC device is additionally connected to the antenna, thereby controlling the impedance matching and achieving a somewhat wide frequency band. However, this method, in which the external circuit is involved in the frequency modulation, causes another problem, such as the deterioration of the antenna efficiency.
FIG. 3 is a perspective view of another conventional chip antenna. With reference to FIG. 3, the chip antenna 10 comprises a body 2 having a hexahedral shape, which is made of dielectric material or magnetic material, a ground electrode 3 formed on one whole surface of the body 2, a radiation electrode 4 formed on at least another whole surface of the body 2, and a power-feeding electrode 5 formed on yet another surface of the body 2. One end 4a of the radiation electrode 4 is opened and is formed adjacent to the power-feeding electrode 5. The one end 4a of the radiation electrode 4 is spaced apart from the power-feeding electrode 5 by a gap 6. The other end of the radiation electrode 4 is branched into multiple sections, thereby forming ground terminals 4b and 4c. The ground terminals 4b and 4c are connected to the ground electrode 3 via different surfaces of the body 2. Japanese Laid-open Publication No. 11-239018 discloses the configuration of this chip antenna in detail.
In the aforementioned chip antenna, compared to other area of the radiation electrode, a short bar for connecting the ground electrode to radiation electrode is very narrow. Therefore, a conduction loss of the radiation electrode is increased at the short bar, thereby deteriorating antenna efficiency. Herein, arrows J1 and J2 indicate a direction of flow of current on the radiation electrode.
FIG. 4 is a plan view of the printed circuit board (PCB) of FIG. 3, showing an antenna portion for mounting an antenna and a generation location of maximum current. That is, FIG. 4 shows the antenna portion for mounting the antenna and the generation location of maximum current, in case the conventional chip antenna is installed on the printed circuit board (PCB) of a mobile communication apparatus. The conventional antenna as shown in FIG. 1 is a short bar type patch antenna, which uses an electromagnetic coupling (EMC) feeding method, and comprises two short bars. Either of two short bars corresponds to the feeding pad. Therefore, when this antenna shown in FIG. 3 is installed on the printed circuit board (PCB) of the mobile communication apparatus, as shown in FIG. 4, the generation location of maximum current (MC) is adjacent to other circuits such as a radio frequency (RF) circuit on the printed circuit board (PCB).
Therefore, in the above-described chip antenna shown in FIG. 3, one short bar is coplanar to the feeding pad, thereby forming a non-linear current path. Thus, the conventional chip antenna improves a cross polarization level, but reduces a co-polarization level, thereby reducing a gain. Further, the conventional chip antenna generates interface with the radio frequency (RF) circuit of the printed circuit board (PCB).